Traumatic arteriovenous fistula of the popliteal artery associated with a closed subtrochanteric fracture: report of a case

Major vascular injuries associated with closed fractures of the femur are rare. A 35-year-old man incurred a subtrochanteric fracture associated with an arterial injury distally. The femoral fracture type most likely to be associated with a major vascular injury is one near the junction of the middle and distal thirds of the bone. The mechanism involves tethering of the artery in the adductor hiatus. The location of the arterial injury is usually at the fracture site.

Laser resonators folded by diffraction gratings

A grating may be employed to fold a laser resonator, thereby enabling the simultaneous extraction of several frequencies from the laser. This limits the range of useful grating constants as compared to the Littrow case. The astigmatism introduced by the grating is examined through the use of sigma-circle diagrams. It will be seen that the grating performs an angle-dependent transformation on the sigma-circle representative of the plane of diffraction to make the mode astigmatic. Some consequences of this related to the design of similar resonators are discussed.